1. Field of the Invention
The present invention relates to a method of detecting surface pressure distribution of a wafer being processed by a CMP (Chemical Mechanical Polishing) process; more specifically, the invention relates to a method of detecting pressure distribution on a wafer surface by employing pressure sensitive films located on various pressure components such as a wafer carrier, a polishing pad, and mechanical arm members of a CMP machine for detecting pressure-related data during different stages of a CMP process so that better pressure components can be designed accordingly.
2. Description of Related Art
In any manufacture of ULSI (Ultra-Large-Scale Integration) devices, a precise and stable CMP (Chemical Mechanical Polishing) process has always been a key in maintaining high production yield. Of all the pressure related components contained in a CMP machine, the electro-static-chuck, the mechanical arm, and wafer clamps on a wafer carrier are the most crucial in directly effecting the yield and finishing quality of the CMP process. Currently, there is no available semiconductor equipment that can provide feedbacks of pressure-related data including image data mapping, numeration, simulation, and forecasting for either manual or automatic surface pressure correction on a wafer.
FIG. 1 shows a frontal view depicting relative positions of a wafer carrier 12, a wafer 10, and a polishing pad 14 of a conventional CMP device. The wafer carrier 12, together with a wafer 10, is to be pushed towards the polishing pad 14 so that exposed surface of the wafer 10 touches the parallel polishing pad surface for a chemical mechanical polishing. The body structure of the wafer carrier is made of steel, and a rubber ring 16 is installed on the working surface of the wafer carrier 12 cushioning a wafer, which is securely held on top of the airtight rubber ring by vacuum pressure during a CMP operation. The vacuum is actuated by evacuating air, with a pump, through a center hole 18 on the wafer carrier 12. A wafer 10 will then stick to the working surface of the wafer carrier 12 when air is pumped out of the center hole 18. The polishing pad 14 is made of composite fiber-like materials knit in various patterns depending on application. The knitting patterns can be of grid pattern, concentric circle pattern, or radiating pattern such that different patterns provide different contacting surface pressure distributions during the CMP process. Further, a number of factors also decide the surface pressure distribution of a silicon wafer during the CMP process, and they are: condition of the rubber ring 16, vacuum efficiency actuated through the center hole 18 of the wafer carrier 12, and material type of polishing pad 14 (such as type of fiber, coefficient of elasticity, fiber size, and weight ratio, etc). The knitting pattern of said polishing pad 14 is of crucial importance in any chemical mechanical polishing process. Therefore, obtaining a database regarding the distribution of surface pressure through sensors located on various pressure related components of a CMP machine can significantly improve the process in development of new components, problem diagnosis, and controlling and maintaining the overall quality of the CMP process.
FIG. 2A and 2B depict simplified frontal views of conventional wafer-manipulating devices such as an electrostatic-chuck or a wafer clamp, so wafers can be conveyed between separate processing chambers securely. For instance, a conventional wafer-manipulating device consists of a mechanical arm with a steel-structured arm members wherein an air opening 24 or a suction cup 24xe2x80x2 is adapted as a gripper to pick up and transfer wafers, one by one, to a specified location. Surrounding the wafer will be a plurality of circularly arranged claws 26 or a vacuum-assisted rubber ring 26xe2x80x2 to prevent any slipping of the silicon wafer during transferring. As it is with any other conventional vacuum-actuated wafer gripping devices, if the vacuum is too weak, the wafer may loose its grip and fall; if the vacuum is too strong, the wafer may warp or even break. Similarly, if the positioning rubber ring 26 or claws 26 are too loose, then the wafer being transferred may fall or somehow be shifted slightly; the opposite of which will cause the wafer to warp or break.
In order to alleviate the aforementioned problems caused by an unevenly distributed surface pressure of a silicon wafer during a CMP process, a method according to preferred embodiment of the present invention is provided to detect surface pressure distribution via pressure sensitive film and obtain image data of surface pressure distribution under different operating conditions for process analysis and correction. Specifically, sensed pressure data are fed to a microprocessor to perform a real-time feedback loop analysis for instant digital image mapping, numeration, simulation, and forecasting, from which more mechanical components of higher precision to be used by the CMP machine can be developed.
Accordingly, it is an object of the present invention to provide a pressure detecting method by placing a plurality of pressure sensitive films located on contacting surfaces of various pressure related components such as the wafer carrier, the polishing pad, and the mechanical arm of a CMP machine for pressure-sensing of a wafer surface during different stages of a CMP process. When a silicon wafer, or wafer, is securely held by the wafer carrier, the pressure-sensing films immediately start to collect pressure-related data during different stages of the CMP process, whereby a corresponding digital image of pressure-related data about the wafer is immediately processed by a computer and displayed by a monitor.
It is another object of the present invention to provide a data analyzing method for processing pressure distribution data of various pressure related components during a wafer CMP process so that suitable input parameter sets for different operating conditions can be established. The established parameter sets are very helpful in improving production yield and efficiency.
Furthermore, pressure distribution data of the pressure related components can be obtained and analyzed at the same time as the pressure distribution data of a wafer are collected. The pressure distribution data on the pressure related components are systematically contrasted and analyzed in order to suitably modify the pressure related components; in addition, it is more convenient to maintain a good working order of the pressure related components with the help of the pressure distribution data set.
According, it is necessary for the present invention to provide a method of pressure detection on the surfaces of the wafer and the pressure related components so that sets of input parameters can be generated by feedback loop analysis for system correction and modification and for further improvements on overall wafer CMP process. Specifically, the invention relates to a method of detecting pressure distribution on a wafer surface by employing pressure sensitive films located on various pressure components such as a wafer carrier, a polishing pad, and mechanical arm members of a CMP machine for detecting pressure-related data during different stages of a CMP process. Such method of wafer pressure detection is accomplished by first providing a pressure related component and a wafer, having pressure sensitive films bonded to the pressure components, subjecting the wafer and the pressure related components to various pressure conditions, applying pressures of different intensity to various surfaces of the sub-assembly, and processing and saving pressure image data collected via the pressure sensitive films. In particular, the pressure image data are captured with a scanner or a digital camera, fed into a computer, and various pressure image data are then compared and analyzed by a microprocessor. Further, the microprocessor is to simulate pressure distribution data on the pressure components under different operating conditions, so optimum controlling procedures can be established according to input parameter sets generated by computer feedback loop analysis. The acquired pressure distribution knowledge is advantageous for further development of new mechanical pressure components, modification of input parameters, and diagnosis of any operational abnormalities.
The pressure sensitive film according to an embodiment of the present invention comprises a color-forming layer and a color-developing layer of polyester base material bonded together as one sheet. Alternatively, the pressure sensitive film can also be of a single layer polyester film with the color-forming material coated to a surface of the film and the color-developing material coated to the other surface. In both cases, the color-forming layer is composed of a plurality of microcapsules of color-forming material.
In addition, the pressure components applied in the embodiment of the present invention refer to, but not limited to, mechanical CMP pressure related components including a wafer carrier, a polishing pad, and mechanical arm members of a CMP machine.